Position sensor and a linear compressor

ABSTRACT

The present invention relates to a sensor, particularly useable for detecting the position of a compressor actuator ( 2 ), the actuator ( 2 ) being axially displaceable in a cylinder bore ( 3 ), the sensor comprising a probe ( 4 ) and a hermetic terminal ( 7 ) associable with each other, the probe ( 4 ) being positioned inside the cylinder bore ( 3 ), the hermetic terminal ( 7 ) being connected to a control circuit ( 8 ) and, further, to a linear compressor provided with an actuator ( 2 ), a cylinder bore ( 3 ) and a head ( 5 ), the actuator being axially displaceable inside the cylinder bore ( 3 ), the linear compressor comprising a position sensor comprising a probe ( 4 ) and a hermetic terminal ( 7 ) associable with each other, the probe ( 4 ) being positioned inside the cylinder bore ( 3 ), the hermetic terminal ( 7 ) being connected to a control circuit ( 8 ).

The present invention relates to a position sensor applicable to alinear compressor and used for detecting the position of the compressoractuator, as well as to a linear compressor provided with a positionsensor.

DESCRIPTION OF THE PRIOR ART

A linear compressor basically comprises an actuator or piston that isaxially displaced inside a cylinder bore and that has the function ofcompressing the gas during the cooling cycle. In order to allow this gasto go in and out,the compressor is further provided with a headcomprising a suction valve and a discharge valve. This head is locatedat the end of the actuator stroke.

The actuator, together with a magnetic component and a resonant spring,forms a resonant assembly that is driven by a linear motor. Thisresonant assembly develops a linear movement, and the axial displacementof the actuator provides the necessary compression of the gas.

If there are variations in operation or variations in the feed voltageof the compressor, the resonant assembly comes out of its normal courseof movement and is displaced beyond the permitted limit, causing theactuator to collide with the compressor head. This abnormality causesnoises and damage to the compressor, especially to the valve head.

One can try to solve this problem by controlling the voltage levelsapplied to the motor or by controlling the displacement of the actuatorin the bored-through body, in order for the latter not to damage thehead.

This control over the displacement of the actuator may also be effectedby positioning the sensor on the head, so that it will signal orinterrupt the energy supply upon detection of the beginning ofcollisions of the actuator against the head. Although this solutionstops the collision of the activator, it does not avoid it from damagingthe head, mainly if a sensor failure happens.

Another solution foreseen for controlling the course of displacement ofthe actuator inside the cylinder bore consists in using a positionsensor, usually inductive transducers that detect the passage of theactuator by a determined control point. The disadvantage of thissolution lies in the high cost of the device used and the difficulty ininstalling and maintaining it, which causes the final cost of thecompressor to rise.

PI 0001404-4 relates to a position sensor placed close to the compressorhead and capable of signaling the passage of the actuator by a maximumrecommendable point, in order to prevent it from bumping against thehead at the moments of variations in its operation. This sensor is madeof an electrically conductor material, which upon receiving contact ofthe actuator emits an electric signal to a control circuit, whichprevents the actuator from continuing its advance towards the valvehead.

However, in order for this solution to be possible, the sensor has to beinsulated from the rest of the compressor, as for instance, from thecylinder bore and from the head, so that the circuit can remain openuntil the actuator leans against the sensor. In the embodiment to whichPI 0001404-4 refers, this insulation may be effected by means of jointsmade of a sealing material and electrically inert, placed at the portionin which the sensor is in contact with the compressor or all over thehead. In this regard, the sensor is manufactured from a blade thatconstitutes the valve and that is positioned on the head.

The use of sealing joints requires an adequate adjustment in thepositioning of the valve blade that has the sensor, of the head and ofthe cylinder bore.

As described in PI 0101976-7, another proposed solution consists inusing a sensor plate independent of the suction valve, but with the sameexternal profile, the electric insulation of this plate being effectedby depositing upon it a painting layer of the epoxy or varnish type, oranother type having electric resistance characteristics. The maindisadvantages of this solution lie in the need for electric insulationthroughout the sensor place and to the possibility of escape of currentdue to the area of the sensor plate.

OBJECTIVES OF THE INVENTION

The objective of the present invention is to provide a sensor capable ofdetecting and controlling the position of the actuator close to the headand to the compressor valves, in order to prevent the actuator frombumping against the head during a failure in its functioning, withoutthis raising the costs of manufacturing the compressor.

BRIEF DESCRIPTION OF THE INVENTION

The objective of this invention is achieved by means of a sensor,particularly useable in detecting the position of an actuator of acompressor in which the actuator is axially displaceable inside acylinder bore, the sensor comprising a probe and a hermetic terminal tobe arranged in a head of the cylinder, the probe being positioned insidethe cylinder bore, the probe and the hermetic terminal being associablewith each other by means of the contact of the actuator with the probe,the hermetic terminal being connected to a control circuit.

The objectives of this invention are also achieved by means of a linearcompressor provided with an actuator, a cylinder bore and a head, theactuator being axially displaceable inside the cylinder bore, the linearcompressor comprising a position sensor comprising a probe and ahermetic terminal, the hermetic terminal being arranged in the head andthe probe being positioned inside the cylinder bore, tho probe and thehermetic terminal being associable with each other by means of thecontact of the actuator with the probe, the hermetic terminal beingconnected to a control circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in greater detail withreference to an embodiment represented in the drawings. The figureshows:

FIG. 1—Is a schematic cross-section view of the linear compressor and ofthe sensor of the present invention.

DETAILED DESCRIPTION OF THE FIGURES

According to a preferred embodiment and as can be seen In FIG. 1, thelinear compressor comprises an actuator 2, which is displaceable insidea cylinder bore 3, and a head 5 positioned at the end of the course ofdisplacement of the actuator 2 and comprising the suction valve 17 anddischarge valve 17′.

The position sensor comprises a probe 4, positioned inside the cylinderbore 3, and a hermetic terminal 7, connected to a control circuit 8.

The probe 4 is thin and flexible and may be constituted by a metallicblade, which may be replaced by a cylindrical, massive or hollow piece,or else may have another appropriate shape. This probe 4 comprises afirst end 11, a contact projection 10, a contact region 9 and a secondend 12. The first end 11 is fixed between the aid 5 and the cylinderbore 3, while the second end 12 is free from engagement.

In a variation of fixation of this probe 4, it is fixed on the actuator2 itself, the first end 11 being fixed on the face of the actuator 2,while the second end 12 remains free from fixation or engagement.

The contact projection 10 is formed from a bending of the body of theprobe 4. This projection 10 is arranged between the first end 11 and thesecond end 12, so as to remain aligned with the hermetic terminal 7.

The contact region 9 is arranged at the second end 12 and has asubstantially curved profile reducing the friction during the contact ofthe actuator 2 with this region 9.

The contact projection 10 and the contact region 9 are arranged ondifferent planes. With respect to the head 5, the contact projection 10has a null spacing since it is permanently in contact with the head 5,as shown in detail A, while the contact region 9 has a spacing h, as canbe seen in detail B of FIG. 1.

The hermetic terminal 7 will be positioned in an insulated cavity 15,filled with an insulating material 16 and arranged on the head 5 of thecompressor.

According to detail A of FIG. 1, the hermetic terminal 7 is mounted inthe cavity 15 at a backset distance d with respect to the surface of thehead 5 facing the interior of the cylinder bore 3. In this way, thepositioning of the hermetic terminal 7 on the head 5 should be carriedout in such a way that the terminal 7 will be aligned to the contactprojection 10, since the probe 4 and the hermetic terminal 7 areassociable with each other by means of the contact of the contactprojection 10 with the hermetic terminal 7. Thus, the end of theterminal 7 that should contact the contact projection 10 is preferablyplane and parallel to the face of the head 5 in order for the curvatureof the contact position 10 to obtain satisfactory contact with this endof the terminal 7. However, other variations in shape of this end of theterminal 7 are foreseen, as for example, the shape of an inclined planeor chamfer with an angle of inclination coinciding with that of theprobe 4, among others.

In addition, the hermetic terminal 7 is connected to the control circuit8, formed by an electric circuit comprising a source of electric voltage21, preferably of direct current, and a resistor 22, both connected inseries with the hermetic terminal 7 and the head 5, as illustrated indetail C of FIG. 1. In one of the possible variations of this circuit,an association of the source 21 and the resistor 22 in series with theterminal 7 and with the actuator 2 is foreseen.

When the actuator 22, in its axial displacement, reaches a determineddistance from the head 6, that is to say, a first control point 6, theactuator 2 contacts the contact region 9 of the probe 4, displacing itas far as the second control point 6′ arranged at a displacementdistance H from the first control point 6.

When the contact region 9 reaches the second control point 6′, thecontact projection 10 is physically in contact with the hermeticterminal 7, forming an electric contact with the control circuit 8. Inthis way, the Contact of the actuator 2 with the contact region 9 issubstantially simultaneous with the contact of the contact projection 10with the hermetic terminal 7.

Said electric contact formed with the control circuit 8, that is, theindication that the actuator 2 has reached the first control point 6 andthe second control point 6′ causes, the voltage level measured at theterminals. (not shown) close to the resistor 22 to pass from the logicallevel “0” to the logical level “1”. This variation is read by thecontrol circuit 8, which may further include an electronic circuitcapable of interpreting this signaling, which corrects the path of theactuator 2, thus preventing it from bumping against the head 5, that isto say, it causes the maximum displacement of the actuator 2 toward thehead 5 to return to below the first control point 6.

Once this excess in displacement of the actuator 2 is corrected, thecontact region 9 is again positioned at the same level as the firstcontrol point 6. For this purpose, the probe 4 should preferably be madefrom a material having an elastic deformation zone that embraces theamplitude of this deformation which the probe 4 undergoes during thisdisplacement of the region 9 from the first control point 6 to thesecond control point 6′. This is because, after the efforts have ceased,the region 9 should necessarily return to its initial position, that isto say, coinciding with the first control point 6.

Thus, the material employed in constructing this probe 4, independentlyof its shape and profile, should be little susceptible to hysteresis,that is to say, to the residual deformations along the time of use ofthe sensor.

The present invention has the advantage of meeting the need for paintingthe sensor plate in an attempt to insulate it from the rest of thecomponents of the compressor, thus increasing the reliability of theinsulation of the probe 4 and providing a more precise control over theposition of the actuator 2.

Another advantage of the present invention lies in the low cost of thehermetic terminal 7 and in its great availability on the market. Forthis reason, the applied modifications do not render the finalcompressor assembly expensive.

A preferred embodiment having been described, one should understand thatthe scope of the present invention embraces other possible variations,being limited only by the contents of the accompanying claims, whichinclude the possible equivalents.

1. A sensor, particularly useable in detecting the position of anactuator (2) of a compressor in which the actuator (2) is axiallydisplaceable inside a cylinder bore (3), the sensor being characterizedby comprising: a probe (4) and a hermetic terminal (7) to be arranged ina head (5) of the cylinder (5), the probe (4) being positioned insidethe cylinder bore (3), the probe (4) and the hermetic terminal (7) beingassociable with each other by means of the contact of the actuator (2)with the probe (4), the hermetic terminal (7) being connected to acontrol circuit (8).
 2. A sensor according to claim 1, characterized inthat the probe (4) comprises a contact projection (10) arranged betweena first end (11) fixed between a head (5) and the cylinder bore (3) anda second end (12).
 3. A sensor according to claim 2, characterized inthat the second end (12) comprises a contact region (9).
 4. A sensoraccording to claim 3, characterized in that the contact region (9)comprises a substantially curved profile.
 5. A sensor according to claim4, characterized in that the contact projection (10) and the contactregion (9) are arranged on different planes.
 6. A sensor according toclaim 5, characterized in that the hermetic terminal (7) is positionedin an insulated cavity (15) arranged in the compressor hood (5).
 7. Asensor according to claim 6, characterized in that the hermetic terminal(7) is positioned at a backset distance (d) from the head (5).
 8. Asensor according to claim 7, characterized in that the probe (4) and thehermetic terminal (7) are associable with each other by means of thecontact of the contact projection (10) with the hermetic terminal (7).9. A sensor according to claim 8, characterized in that the contact ofthe contact projection (10) with the hermetic terminal (7) forms anelectric contact with the control circuit (8).
 10. A sensor according toclaim 9, characterized in that the contact region (9) is contactable bythe actuator (2).
 11. A sensor according to claim 10, characterized inthat the contact of the contact projection (10) with the hermeticterminal (7) is substantially simultaneous with the contact of theactuator (2) with the contact region (9).
 12. A sensor according toclaim 11, characterized in that the substantially simultaneous contactof the contact projection (10) with the terminal (7) and of the actuator(2) with the contact region (9) takes place substantially at a firstcontrol point (6).
 13. A sensor according to claim 11, characterized inthat the substantially simultaneous contact of the contact projection(10) with the terminal (7) and of the actuator (2) with the contactregion (9) takes place at a second control point (6′).
 14. A sensoraccording to claim 12 or 13, characterized in that the control circuit(8) comprises an electric circuit that includes a source of electricvoltage (21) and a resistor (22), both connected in series with thehermetic terminal and with the head (5), the electric circuit beingclosed when the contact projection (10) contacts the hermetic terminal(7).
 15. A sensor according to claim 12 or 13, characterized in that thecontrol circuit (8) comprises an electric circuit that includes a sourceof electric voltage (21) and a resistor (22), both connected in serieswith the hermetic terminal (7) and with the actuator (4), the electriccircuit being closed when the contact projection (10) contacts thehermetic terminal (7).
 16. A linear compressor provided with an actuator(2), a cylinder bore (3) and a head (6), the actuator being axiallydisplaceable inside the cylinder bore (3), the linear compressor beingcharacterized by comprising: a position sensor comprising a probe (4)and a hermetic terminal (7), the hermetic terminal (7) being arranged inthe head (5) and the probe (4) being positioned inside the cylinder bore(3), the probe (4) and the hermetic terminal (7) being associable witheach other by means of the contact of the actuator (2) with the probe(4), the hermetic terminal (7) being connected to a control circuit (8).17. A compressor according to claim 16, characterized in that the probe(4) comprises a contact projection (10) arranged between a first end(11) fixed between the head (5) and the cylinder bore (3) and a secondend (12).
 18. A compressor according to claim 17, characterized in thatthe second end (12) of the probe (4) comprises a contact region (9). 19.A compressor according to claim 18, characterized in that the contactregion (9) comprises a substantially curved profile.
 20. A compressoraccording to claim 19, characterized in that the contact projection (10)and the contact region (9) are arranged on different planes,
 21. Acompressor according to claim 20, characterized in that the hermeticterminal (7) is positioned in an insulated cavity (15) arranged in thehead (5).
 22. A compressor according to claim 21, characterized in thatthe hermetic terminal (7) is positioned at a backset distance (d) fromthe head (5).
 23. A compressor according to claim 22, characterized inthat the probe (4) and the hermetic terminal (7) are associable witheach other by means of contact of the contact projection (10) with thehermetic terminal (7).
 24. A compressor according to claim 23,characterized in that the contact of the contact projection (10) withthe hermetic terminal (7) forms an electric contact with the controlcircuit (8).
 25. A compressor according to claim 24, characterized inthat the contact region (9) is contactable by the actuator (2).
 26. Acompressor according to claim 25, characterized in that the contact ofthe contact projection (10) with the hermetic terminal (7) issubstantially simultaneous with the contact of the actuator (2) with thecontact region (9).
 27. A compressor according to claim 26,characterized in that the substantially simultaneous contact of thecontact projection (10) with the terminal (7) and of the actuator (2)with the contact region (9) takes place at a first control point (6).28. A compressor according to claim 26, characterized in that thesubstantially simultaneous contact of the contact projection (10) withthe terminal (7) and of the actuator (2) with the contact region (9)takes place at a second control point (6′).
 29. A compressor accordingto claim 27 or 28, characterized in that the control circuit (8)comprises an electric circuit that includes a source of electric voltage(21) and a resistor (22), both in series with the hermetic terminal (7)and with the head (5), the electric circuit being closed when thecontact projection (10) contacts the hermetic terminal (7).
 30. Acompressor according to claim 27 or 28, characterized in that thecontrol circuit (8) comprises an electric circuit that includes a sourceof electric voltage (21) and a resistor (22), both connected in serieswith the hermetic terminal (7) and with the actuator (2), the electriccircuit being closed when the contact projection (10) contacts thehermetic terminal (7).